"I think the hardest part of my job is working with young people where the perpetrator has been to court and been acquitted," says Sue Woodbridge, children's counsellor at the Coventry Rape and Sexual Abuse Centre.

"The child has steeled themselves to give evidence, they've spoken out, they've been brave ... it's a double betrayal by the perpetrator and then by the criminal justice system, in their eyes."

Sitting in the colourful, toy-filled therapy room in the centre's newly refurbished basement offices, Woodbridge is calmly explaining how she works with some of the youngest victims of sexual abuse. It feels warm and safe down here, and it needs to because this is where children aged from five to 11 come to begin the process of healing the trauma they've undergone, often at the hands of those they trusted most in the world.

Any child who comes here is assured that they are in a safe space, that they're believed, and that they don't have to protect anyone. Being able to express themselves without inhibition is vital in a situation where a family has often been fractured and where the safe carer – usually the mother – may be enduring their own emotional torment.

Children, Woodbridge observes, do not want to add to a parent's pain, and so sessions are almost always held without anyone else present so that that the focus remains entirely on the child.

During a session, "you might see Playmobil all over the floor, us making things, play 'cooking', or me taking part in child-directed role play", she explains. Her role is "about understanding the feelings and processing what's going on in the play. I'd be doing a lot of talking about what I'm observing, so narrating what they're doing to bring it into the awareness of the child what's going on."

Nicki Stott, practice manager for the 5-11 service, observes that "what we often get in the room is the mixed feelings about their abuser".

"You'll get the child trying to play the different roles, being nice to a doll, and then throwing the doll across the room shouting 'bad baby!' "

Though it feels utterly wrong to say so, the children who come here are the lucky ones. In Coventry, there is no other specialist help on offer for a very young child who has suffered sexual abuse. It's the same story across most of the country; until recently, the NSPCC provided expert therapy for the very youngest victims of sexual abuse, but it has recently refocused its work on prevention.

The charity continues to offer play-based therapy to five to 18-year-olds at 18 sites in England, Northern Ireland and Wales. It expects to work with 900 children over the next two years, during which time it will assess the evidence for the effectiveness of this type of therapy. However, if you don't live near one of those 18 sites, there's now nothing much else on offer, apart from what your local voluntary sector is able to provide.

"What GP surgeries can offer – typically, the short term, cognitive therapy model – isn't suitable for a traumatised child," says Dianne Whitfield, the centre's director. "The only other way you'd get statutory help is if you have a mental health diagnosis, through Camhs (the child and adolescent mental health service).

"Our experience is that statutory thresholds have got higher and tighter," she continues. "For instance, we had a referral from a GP who said his patient had been refused by Camhs and told us there was nowhere else to go."

Jon Brown, head of the NSPCC's sexual abuse programmes, says that with between 55,000 and 60,000 children in need of specialist support to deal with the fallout of sexual abuse, the lack of statutory provision is "a scandal ... it is a public health problem, and it needs to be dealt with like that".

Facing a situation where local provision was about to disappear, however, Whitfield knew she had to act fast. The 2010 Alberti report on violence against women and children suggests that 11% of boys and 25% of girls under 16 will have experienced sexual abuse. That's 9,500 in Coventry alone. And the centre's experience helping young women – and more recently, young men – meant it had a keen understanding that if trauma isn't processed early, it can lead to years of anguish and, for many people, blighted lives.

Whitfield also knew she needed to recruit some highly specialist skills: a child of five or six cannot respond to techniques appropriate for teenagers or adults.

"Children don't have the cognitive understanding or the vocabulary to explain what's happened to them," says Woodbridge, who took up her new post in March. "There's confusion. Their world view has been shattered. At that age, they don't always know that abuse is bad – although, often at a later stage, they do understand."

Abuse that happens to young children, Whitfield says, will commonly have shaped a significant proportion of their lives. It becomes their norm. "Many will have gone through a lot. Hearing things like 'If you don't do this, I will do it to your little sister or I will kill your mother'," she says.

And there is also, often, a sense of guilt.

"Children have a misguided belief that they're at fault," says Woodbridge. "They can be told 'It's not your fault', but unless children come to believe that in their very core, they can't move on."

The sessions that take place in this room aim to help children make the journey from a place where they're a victim to a future where they're a survivor. Experience shows that as they grow up, "they will still grieve terribly for the loss of their childhood", Whitfield says, but therapy means they've got a chance to be "no longer absolutely defined by that act".

Children can be referred to the Coventry centre by anyone, but most often, for this age group, it will be social services, police, teachers or multi-disciplinary teams that get in touch. There is only enough funding for two part-time counsellors, and Woodbridge and her colleague manage a caseload of six children each. The youngest who's been seen since the service launched in March was four years old. And, inevitably, there's a waiting list.

It's important that children know that their therapy sessions don't go on for ever; defining and respecting boundaries is part of rebuilding their trust in the world. The initial contract will be for six sessions, which can be extended if necessary, but again a time-limit is always explained and agreed.

Does the need for this kind of specialist therapy ever finish when a child has experienced abuse?

"My feeling is that it might be finished 'for now', and a child will then take a period of time to consolidate what they've worked on," says Woodbridge. "Children can come back as many times as they need to.

"Sometimes," she adds, "a child thinks they're the only person in the world this has happened to, so realising that there's a whole service dedicated to it helps them, I think."

As reported instances jump 22%, local authorities have a big task – from ensuring a collaborative system operates so signs of abuse are spotted to providing 'safe houses' and counselling. Ben Cook reports